I have spent most of my time on starmade simply building, and I think i can afford to pass on a few tips that I have/used in the past. Biggest being dont be afraid to build what ever you want, dont let others tell you how to build your ships, sure taking advice from others helps, but if someone says that a part of your ship is bad, go build it like so and so does, then just ignore them. its your ship, build it however you damn well please.
as MrFurb has stated looking for concept ideas for what your building or trying to decorate is a good thing to do when you low on ideas, a few of my own creations have been based around ideas or concepts that someone else has tried to do.
Dont be afraid to ditch a ship that just isnt working for you, save it as a blueprint so you can work on it later if you really need to. i have heaps of ships that i have never finished but are stored as blueprints so that i can work on them at a later date should i ever want to.
Be very mindful of what direction your ship core is facing when you go to build it, so many people have built their ships backwards and its not fixable, unless you use something like a 3rd part editing program like SMEdit (i think thats what it is called, if not someone in the public chat should know) Also dont forget you can build with ABM (Advanced Build Mode) and also you can use symmetry to build your ships just that much faster.
Also dont be afraid to try something new, the game is about endless possibilities and is always changing and evolving, so there is no reason why you cant evolve as you play the game, so go on, go out there and have fun, build ships, ruin other peioples ships. I shall try and add more tips if i think of more. so have fun guys.